1. Field of the Invention
This invention relates to a process for an organic photo-voltaic device, and more particularly to a microwave annealing method for plastic substrates.
2. Description of the Prior Art
Most of the electric devices (for example, LEDs, transistors, solar cells) are fabricated on silicon wafers or glass substrates with high temperature resistant. The applications of the substrates have many constraints due to hardness and unyielding property of the substrate. Therefore, an organic electron material with relatively low processing temperature as an active layer material may be easily fabricated on a plastic substrate to achieve the advantages of light-weightiness, low processing temperature and flexibility electric device, and thereby various organic electron devices having widely used.
With the technical development, some electric devices may be made by an organic material, for example organic thin film transistor (OTFT). In comparison with the conventional inorganic transistor, organic thin film transistors may be made at low temperature, and therefore the processed substrate may be selected by light-weightiness, thinner and low cost plastic substrates replacing glass substrates. Moreover, the organic thin film transistors have simply fabricating process by printing method for patterning an organic film to reach the purpose of reducing mask number and without vacuum deposition equipment. The process of fabricating an organic thin film transistor on a plastic substrate is compatible with a roll to roll process, and therefore it has a great benefit of reducing the manufacturing cost.
Recently, because conjugated polymer semiconductors exhibit many advantages such as cost-effectiveness and feasibility to scale up, their applications in organic light-emitting diodes, organic thin-film transistors and organic solar cells have been intensively studied. When fabricated on plastic substrates, further advantages such as flexibility, light-weightiness, easy to carry, not easy to break can be obtained. Furthermore, because of the flexibility, continuous roll-to-roll processing may be employed to lower the processing cost and increase the throughput. However, because of the constraints of plastic substrates such as glass transition temperature and high coefficient of thermal expansion, the processing temperature need to be limited to low temperature, for otherwise warpage and degradation may result. Therefore, how to achieve effective annealing at reduced temperature is imperative.
Currently, processing of most of the organic devices is used to hot-plate annealing to improve the performance of the organic devices. However, hot-plate annealing the organic devices fabricated on the plastic substrates will create negative impact, for example, warpage and degradation of the plastic substrates to cause adverse effects for the subsequent process. Moreover, hot-plate annealing exhibits much higher energy loss and low efficiency of energy usage.
In view of the aforementioned drawbacks, the present invention provides an improved method for solving issues of warpage and degradation of the substrates and negative impact caused by hot-plate annealing.